The present invention, in some embodiments thereof, relates to surgical methods and devices, and, more particularly, but not exclusively, to methods and devices for precise ablation of tissue.
The present invention opens up a wide variety of applications, some of which were historically implemented by use of a pulsed laser.
Pulsed CO2 lasers are generally considered to be precise surgical tools for non-bleeding incision and ablation of tissue. Lasers such as the “Ultrapulse” CO2 lasers are capable of char-free vaporizing a crater in tissue with collateral thermal damage of 50-100 microns. Such low collateral thermal damage is desired in applications such as neurosurgery, gynecology and aesthetic skin resurfacing, where scarring is undesirable. CO2 lasers ablate or incise tissue by removing subsequent layers of tissue, each layer being approximately 30-50 microns deep, based on power and duration of the CO2 laser pulse, and other considerations. CO2 lasers are often used in a focused mode, with a focused beam of spot size of 50-300 microns.
For better understanding some embodiments of the present invention, as illustrated in FIGS. 2-17 of the drawings, reference is first made to FIG. 1 which is a simplified drawing of a prior art pulsed CO2 laser 5 being used for ablation of tissue 10 by vaporization.
FIG. 1 depicts a simplified view of operating principles of a prior art, ablative, char-free, surgical, pulsed CO2 laser 5.
The CO2 laser 5 is depicted in a first view at the top right of FIG. 1. The first view includes a CO2 laser unit 6, an articulated arm 7 with an optic path or an optic fiber for directing a laser beam 17 from the CO2 laser unit 6 to the tissue 10.
A second, enlarged, view at the left and bottom of FIG. 1 depicts an enlarged view of the beam 17 and a cross section of tissue 10.
The beam 17, the spot size of which may be 50-500 microns in diameter, is delivered from the pulsed CO2 laser unit 6 to a surface of the tissue 10. The pulse duration is usually between 100 microseconds to 5 milliseconds. The optical beam 17 is absorbed by the tissue 10 down to a depth of approximately 30-50 microns. The absorbed optical beam 17 is transformed into thermal energy. The energy density of the optical beam 17 is typically selected to be above approximately 5 Joules/cm2, which causes vaporization of the tissue 10 at a rate which exceeds the diffusion rate of heat into the tissue 10. As a result, a crater 15 is produced in the tissue 10, while the bulk of the tissue 10 which is vaporized is transformed into vapors 13, which are flushed. A collateral thermal damage zone 19 around the crater 15 is approximately from 50 to 150 microns deep, which is a diffusion depth of heat into the tissue 10 during a duration of a few milliseconds.
In a case where the tissue 10 is skin, FIG. 1 also depicts a layer 11 called papillary dermis. In a particular application of skin resurfacing, where an external surface of the skin is vaporized, it is usually desired to avoid any ablation of skin below a depth d of approximately 100-150 microns, which is the depth of the papillary dermis, in order to avoid scarring.
In other applications, such as very precise incisions, such as an eyelid incision, it is possible to drill deeper into the tissue, down to a tissue layer 14, by repeating the ablation of thin layers at the treatment site. Ablation of a surface of the skin, or of any tissue, by the CO2 laser is typically performed by repeating the vaporization process described above with a scanner which moves the beam over the skin, or by using a large spot size beam. An example of large spot size beam can be a 10 mm diameter beam, which can still have an energy density above approximately 5 Joules/cm2). Precise incisions are performed by a CO2 laser by sequentially moving the beam in a linear or curved path.
U.S. Pat. No. 5,123,028 describes the Ultrapulse CO2 laser, and U.S. Pat. No. 5,360,447 describes hair transplantation with the Ultrapulse CO2 laser.
U.S. Pat. Nos. 5,411,502, 5,423,803 and 5,655,547 also describe CO2 lasers for scar free incision and ablation of tissue with a focused beam. CO2 laser beams can also be delivered to tissue through optical fibers. This is particularly useful for ablating tissue in minimal invasive procedures such as diskectomy
Pulsed Erbium lasers operating at a wavelength of approximately 3 microns are also considered as superficial skin ablators. The pulsed Erbium lasers operate with large spot sizes (1-10 mm), and vaporize layers of approximately 10 microns of tissue. The pulse duration of erbium lasers is approximately 100-300 microseconds. Pulsed Erbium lasers are used as tools for professional peeling of skin when fast healing is desired (from a few hours to 1-2 days, and enabling patients to be back at work on the same day), due to a capability to operate above the papillary dermis without damaging the papillary dermis. In some countries performance of such peeling is allowed even by aestheticians, rather than physicians.
Additional background art also includes:
US Patent Application 2009/0156958 of Mehta et al;
US Patent Application 2009/0112205 of McGill et al;
US Patent Application 2009/0036958 of Mehta et al;
US Patent Application 2008/0312647 of Knopp et al;
US Patent Application 2008/0281389 of Knopp et al;
US Patent Application 2008/0091185 of McGill et al;
US Patent Application 2008/0091184 of Knopp et al;
US Patent Application 2008/0091183 of Knopp et al;
US Patent Application 2008/0091182 of Mehta et al;
US Patent Application 2007/0191827 of Lischinsky et al;
US Patent Application 2003/0109802 of Laeseke et al;
U.S. Pat. No. 6,475,138 to Schechter et al;
U.S. Pat. No. 6,296,639 to Truckai et al;
U.S. Pat. No. 5,733,278 to Slatkine et al;
An article on CO2 laser skin resurfacing by Chernoff G. et al, entitled “SilkTouch: a new technology for skin resurfacing in aesthetic surgery”, published in J Clin Laser Med Surg. 1995 Apr.; 13(2):97-100;
An article by Lowe N J, et al, entitled “Skin resurfacing with the Ultrapulse carbon dioxide laser—Observations on 100 patients” published in Dermatol. Surg. 1995 Dec.; 21(12):1025-9;
A World Wide Web site for thermal conductivity coefficients of various metals: www(dot)engineeringtoolbox(dot)com/thermal-conductivity-metals-d_858 (dot)html; and
A World Wide Web site for heat capacity of metals: www(dot)engineeringtoolbox(dot)com/specific-heat-metals-d_152(dot)html